Feature: add user-defined index access method origin

[hw118118]

The purpose of the commit is in support of user-defined index access method. Currently, there are many restrictions for index access methods and new index access methods are incompatible with internal framework. At the same time, it's impossible for user to change default index access method. So I build some hooks that are for changing default behavior and being compatible for those strange restrictions.

For express the meaning of the modification, I show a example as below.

For example , I want to add 7 kinds of new index access method that based on diffrent storage engine (maybe unionstore storage) and they are correspond to internal index access methods as below:

• usbtree ---btree
• usgin --- gin
• usgist --- gist
• usspgist --- spgist
• ushash --- hash
• usbitmap --- bitmap

The main diffrence between them is index data can separate from other data and support Compute and Storage Separation.

Suppose we want to use these new functions, we can create a new extension and we can run sql （for example by create extension unionstore;) command and you can find new access methods :

regression=# select * from pg_am;
  oid   |    amname     |         amhandler         | amtype
--------+---------------+---------------------------+--------
      2 | heap          | heap_tableam_handler      | t
    403 | btree         | bthandler                 | i
    405 | hash          | hashhandler               | i
    783 | gist          | gisthandler               | i
   2742 | gin           | ginhandler                | i
   4000 | spgist        | spghandler                | i
   3580 | brin          | brinhandler               | i
   7024 | ao_row        | ao_row_tableam_handler    | t
   7166 | ao_column     | ao_column_tableam_handler | t
   7013 | bitmap        | bmhandler                 | i
  16394 | union_store   | heap_tableam_handler      | t
  16402 | ushash        | ushashhandler             | i
  16403 | usbtree       | usbthandler               | i
  16404 | usgist        | usgisthandler             | i
  16405 | usgin         | usginhandler              | i
  16406 | usspgist      | usspghandler              | i
  16407 | usbrin        | usbrinhandler             | i
  16408 | usbitmap      | usbmhandler               | i
  22820 | heap2         | heap_tableam_handler      | t
 111831 | ao_row_testam | ao_row_tableam_handler    | t
 111847 | ao_col_testam | ao_column_tableam_handler | t
 111850 | heap_testam   | heap_tableam_handler      | t

So you can use these new index access methods as internal index access method. At the same time, I add new guc variable and you can correct default index type by set default_index_type = usbtree or show relevant info by show default_index_type;

In conclusion, it's more flexible and it decoupe from other part.

[avamingli]

Shall we add cases to test new hooks?

[avamingli]

Hi, I test the branch with the added GUC, there are sth we need to fix.

1. set default_index_type, and create a new index, the GUC doesn't take effect.
   We set it to brin, but new created index is also btree.

gpadmin=# set default_index_type = brin;
SET
gpadmin=# show default_index_type;
 default_index_type
--------------------
 brin
(1 row)

gpadmin=# create index on t2(c1);
CREATE INDEX
gpadmin=# \d+ t2;
                                           Table "public.t2"
 Column |  Type   | Collation | Nullable | Default | Storage | Compression | Stats target | Description
--------+---------+-----------+----------+---------+---------+-------------+--------------+-------------
 c1     | integer |           |          |         | plain   |             |              |
 c2     | integer |           |          |         | plain   |             |              |
Indexes:
    "t2_c1_idx" btree (c1)
Distributed by: (c1)
Access method: heap

2. We lack of test when setting this GUC to check the invalidation.
   User could set a not-exists value, it's risky.

gpadmin=# select * from pg_am;
 oid  |  amname   |         amhandler         | amtype
------+-----------+---------------------------+--------
    2 | heap      | heap_tableam_handler      | t
  403 | btree     | bthandler                 | i
  405 | hash      | hashhandler               | i
  783 | gist      | gisthandler               | i
 2742 | gin       | ginhandler                | i
 4000 | spgist    | spghandler                | i
 3580 | brin      | brinhandler               | i
 7024 | ao_row    | ao_row_tableam_handler    | t
 7166 | ao_column | ao_column_tableam_handler | t
 7013 | bitmap    | bmhandler                 | i
(10 rows)

gpadmin=# set default_index_type = not_exist;
SET
gpadmin=# show default_index_type;
 default_index_type
--------------------
 not_exist
(1 row)

gpadmin=# create table t3(c1 int unique, c2 int);
ERROR:  access method "not_exist" does not exist

3. We changed the codes when creating a table in parse stage.
   But doesn't have a case to check, like

create unique index on t3(c1);

And as the GUC is added by CBDB, we should put it in guc_gp.c, not guc.c
I see the GUC is only used at parse stage, does it need to sync to segments(src/include/utils/sync_guc_name.h)?

[avamingli]

Add some test cases?

[hw118118]

Add some test cases?

There are many test cases but place into extension UnionStore, because it mainly comply with UnionStore extension.